The present invention relates to a a frequency-shift-keying continuous-wave radar. It can be applied especially to radars equipping automobiles and more generally radars requiring low manufacturing cost.
A frequency-shift-keying, continuous-wave radar can transmit in several frequencies, for example four or even more frequencies. A radar of this kind may be fitted for example into an automotive cruise control or ACC type function. A radar of this type is designed to enable the regulation of the behavior, namely the acceleration, speed and braking, of automobiles. It detects and localizes the closest vehicle located in the path of the carrier vehicle. The information, especially information pertaining to distance, is transmitted for example to a computer which acts, through appropriate interfaces, on the control of the engine so as to regulate the distance between the vehicle and its predecessor.
A radar designed to equip an automobile, which is a mass consumer product, has to be low in cost. This low cost is achieved if all the components of the radar are obtained, economically. It is necessary in particular to obtain a low-cost receiver. This goal may be achieved especially by the use of a digital receiver having few components. For this purpose, it is judicious to use only one encoder for the digital conversion of the reception signal. In a frequency-shift-keying receiver, the distance D from the radar to a target may be given by the following relationship:       Δ    ⁢          xe2x80x83        ⁢    ϕ    =                    4        ⁢                  xe2x80x83                ⁢        π        ⁢                  xe2x80x83                ⁢        D            c        xc3x97    Δ    ⁢          xe2x80x83        ⁢    F  
where c is the velocity of light and xcex94F and xcex94xcfx86 respectively are the difference in frequency and the difference in phase between two successive signals.
The use of a single encoder for all the reception channels, one reception channel being associated with one frequency, implies that the operations of sampling the signals of the different reception channels can no longer be synchronous but, on the contrary, sequential. Now, the absence of synchronism between these signals causes the existence of an additional phase shift due to the Doppler effect which disturbs the measurement of distance. In fact, this effect may be corrected after fast Fourier transform operations, known as FFT operations, on the reception signals. However, again for reasons of ease of implementation and therefore of cost, it is preferable to perform the correction before the processing by FFT. Indeed, this averts the need, subsequently, to carry out a differentiated correction pertaining to each Doppler filter.
It is an aim of the invention in particular to enable this correction to be performed upline and therefore to enable the making of a economical receiver for a frequency-shift-keying continuous-wave radar for the detection of distances between moving objects, this receiver being capable of working with a single encoder, by bringing into play the extrapolation of the sampled signals. To this end, an object of the invention is a receiver for a frequency-shift-keying continuous-wave radar transmitting in several frequencies and comprising several corresponding reception channels, wherein said receiver comprises at least sampling means taking real samples of the signals in each reception channel and extrapolation means, the extrapolation means producing fictitious samples synchronous with the real samples, the reception signals being formed out of real samples and fictitious samples.
The main advantages of the invention are that it improves the filtering of the reception signals, is adapted to any number of transmission frequencies, enables the information output rate and the sampling frequency to be made independent of each other, limits the dynamic range of the encoder, facilitates self-calibration, prevents temporal drifts and is simple to implement.